I've come to a conclusion about the Fretless Bass Track. I mean I know someone will find it tomorrow and I'll be wrong, but for now, this is my theory. I think it's BoC.
So, the point of the Societas X Tape was probably to say "look at all the great musical gems that are out there if you go off the beaten tracks". And what did we do? Instead of taking the lesson to heart and going out to find our own gems we pored over every second of the tape tracking down all the sources they used, because *of course we did*.
But I reckon BoC knew by now we'd do that, so they snuck one track on there from their archives, knowing that we'd go mad trying to find it (it's like the old trick about letting loose three pigs numbered 1, 2 and 4 so everyone spends hours searching for pig #3). In the process of hunting we'd do what we were meant to do, listening to all manner of obscure shit.
Like I say, I'm probably well wrong here but for now that's what I'm sticking to, and I'm keeping looking in the knowledge I'll probably never find it because the search is the prize.